'Disappearing everywhere': The great extinction happening under our noses

Insect populations are "threatened worldwide", with only resilient species such as urban cockroaches bucking a trend that has significant implications for animals that rely on them, Australian-based researchers say.

While butterflies might inspire poets and even beetles foster empathy, many are in sharp decline compared with generalist and resilient species such as roaches that are highly adaptable and at home in forests and cities alike.

Urban cockroaches might do well amid a collapse of insect populations globally.Credit:Pat Scala

While Australia's insects are most likely tracking the same downward spiral as in Europe and North America, given the use of similar farm chemicals, poor knowledge of local species makes it harder to gauge the impact of the decline, Francisco Sanchez-Bayo, an honorary associate at the University of Sydney, said.

Australian entomologists "are a rare species themselves", Dr Sanchez-Bayo said. "We cannot do studies long term and we can’t do it all across Australia – it’s too big. We don’t have the human resources."

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He estimated that just 30 per cent of Australian insect species had been identified. Scientist job cuts, including at government agencies, made it harder to monitor populations of known species, let alone identify new ones.

Dr Sanchez-Bayo and Kris Wyckhuys report in the April edition of the Biological Conservation that a third of all insect species are threatened in the countries studied. The total biomass of insects is also declining at the rate of 2.5 per cent globally, the review of 73 historical reports found.

The paper identified habitat loss - such as the spread of cities and intensification of farming - increased use of long-lived pesticides and other agricultural chemicals, the rise of pathogens, and climate change as the main factors behind the decline.

"The general public don’t regard insects are important - they regard them as a nuisance," Dr Sanchez-Bayo said. "It’s a reality - insects are disappearing everywhere."

In fact, insects are critical for pollination, recycling materials in the soil and purifying the water. They also provide the main source of food for birds, bats, fish and many other vertebrate species that typically attract more scientific interest and public sympathy.

Macleay's Swallowtail, one of the butterflies found around Canberra.Credit:Suzi Bond

"If we deplete the food source, as is happening now, all of these animals will go to starvation," Dr Sanchez-Bayo said. "They will disappear simply because they don’t have food."

'The other 99%'

Richard Kingsford, director of the Centre for Ecosystem Science at the University of NSW, said invertebrates were often referred to as "'the other 99 per cent" because they make up most of the world's biodiversity.

Francisco Sanchez-Bayo

"They are a bit out of sight, out of mind when we measure and monitor biodiversity focusing on the megafauna - birds, mammals, reptiles, frogs and fish - but they are what makes the environmental world tick," Professor Kingsford said.

"They do lots of things for humanity that cost us nothing. And they are essential for the future of the planet," he said, adding the new paper captured "a worldwide trend in alarming declines in biodiversity".

Dr Sanchez-Bayo said much of the public can sense from everyday experiences that insect numbers have been on the skids.

He said driving in the Australian bush used to fill windscreens with insects. By contrast, a recent road trip from Sydney to Cooma in the Snowy Mountains left a windscreen that was "untouched".

'Too much pesticides'

While his paper with Dr Wyckhuys focused largely on research from North America and Europe, the likelihood is that insect population declines related to pesticide use is higher elsewhere, such as in Africa and South America.

An Australian bearded dragon waits patiently for a cricket to become lunch.Credit:AP

"The farmers are using too much pesticides," he said. "So the impact those farming practices are having in those countries is probably much larger than the impact they are having in European countries and North America."

Farmers need to "revert to the way we did things in the past", Dr Sanchez-Bayo said, such as reintroducing hedge rows or other habitats to foster diverse species - some of which would control insects without chemicals.

Broadacre cropland, such as on the Liverpool Plains of NSW, has removed crucial habitat for insects and other animals.Credit:Tamara Voninski

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While climate change would increase the range for certain insects, the impact for other regions was likely to be negative, especially in the tropics.

"We know insects in tropical areas are less resilient to changes in temperature," he said.